Edward II recalled Piers from the exile imposed on him by Edward I immediately after he heard the news that his father was dead, on 11 July 1307. Piers was back in England by early August, and Edward created him earl of Cornwall on 6 August, possibly without Piers' prior knowledge - or so Edward would claim in letters to the Pope and the king of France the following year. (Edward can't entirely be trusted here, however - he also claimed that he made Piers an earl at the urging of his barons - which was emphatically not the case!)
Edward also arranged Piers' marriage to his (Edward's, not Piers', obviously) niece Margaret de Clare, which took place on 1 November 1307, but which had been planned for months - the charter granting the earldom of Cornwall to Piers on 6 August was decorated with the de Clare arms as well as Piers' own. Piers had an annual income of £4000, making him one of the richest men in the country.
As though all this wasn't bad enough - making the younger son of a minor Gascon noble a wealthy earl and a member of the royal family by marriage - Piers dominated Edward's favour and attention. According to the contemporary Vita Edwardi Secundi, Piers "alone found favour in the king's eyes and lorded it over them [the English barons] like a second king, to whom all were subject and none equal. Almost all the land hated him..his name was reviled far and wide...he was an object of mockery to almost everyone in the kingdom." The comment that Piers was 'like a second king' is echoed in other chronicles - the (later) Meaux chronicle called him "almost a king" (quasi rex) and the canon of Bridlington claimed there were two kings in England.
Edward's obsession with his friend was such that he refused to see any of his barons unless Piers was also present, and rudely ignored them, talking only to Piers. Piers grew more and more arrogant because of Edward's favour, according to the Vita: "scornfully rolling his upraised eyes in pride and in abuse, he looked down upon all with pompous and supercilious countenance…indeed the superciliousness which he affected would have been unbearable enough in a king’s son."
According to the Flores Historiarum, Piers "aroused the hatred of nearly all the great lords of England, because the new king loved him excessively and irrationally, and supported him totally." On 26 December 1307, Edward took the extraordinary step of appointing Piers custos regni, keeper of the realm or regent, while he went to France to marry Isabella. The Vita spoke for many when its author exclaimed "An astonishing thing, that he who had lately been an exile and outcast from England should now be made ruler and guardian of the realm."
On arriving in England with Isabella, Edward II caused a scandal by rushing up to Piers at Dover, hugging and kissing him repeatedly, in front of everyone. His antics at his coronation strengthened the already strong opposition to Piers, and at the parliament that met at Westminster a few days later, a powerful confederation of earls and barons demanded Piers' exile. They were led by Henry de Lacy, earl of Lincoln, the eldest and most senior earl, a staunch royalist but deeply concerned by Edward's obsession with Piers.
Edward had few allies at this time. One of them was, surprisingly, his cousin the earl of Lancaster (Lincoln's son-in-law) who would later become his greatest enemy, and another their cousin the earl of Richmond, who was politically insignificant. Others were: Roger Mortimer (yes, that Roger Mortimer), Hugh Despenser the Elder, John, Lord Hastings, Edward's former tutor Guy Ferre, William Latimer, John Haudlo, John Cromwell, and John de Sulleye - a few lords and knights who were no match for the grand opposition to Edward and Piers, who were supported to some extent by Edward's powerful father-in-law the king of France.
To cut a very long story short, Edward agreed to exile Piers on 18 May; it had taken him many weeks to give in, and he had little choice, as he was facing civil war. The Vita said "the seditious quarrel between the lord king and the barons spread far and wide through England, and the whole land was much desolated by such a tumult…The king had his towns and castles munitioned and repaired, and the magnates on their part did likewise…it was held for certain that the quarrel once begun could not be settled without great destruction." A letter written around this time agreed: "very evil are the times in England now; and there are many who fear that worse times are still in store for us." (Ironically, the letter was written by Walter Stapeldon, bishop-elect of Exeter, murdered by a mob in 1326 for his loyalty to Edward II.)
The day after Edward finally agreed to the exile, the archbishop of Canterbury threatened to exile Piers if he didn't leave the country by 25 June. Piers' young wife Margaret de Clare was not included in the exile - she was the granddaughter of the old king and the sister of the earl of Gloucester, and nobody intended her any harm or insult - but she accompanied Piers abroad anyway, according to the Lanercost chronicle and the Annals of Dublin. This hardly suggests that their marriage was a disaster or that she hated Piers.
Piers was stripped of the lands he held as earl of Cornwall, though he was allowed to keep the title, an empty gesture probably insisted on by Edward II. A few days after Edward agreed to the exile, he granted Piers £2000 worth of lands in his homeland of Gascony, and another £2000 of English lands to Piers and his wife Margaret jointly - so Piers did not suffer from any loss of income. Edward also gave him a gift of 1180 marks, about 786 pounds, a truly enormous sum.
On 16 June, Edward hit on the idea of making Piers Lord Lieutenant of Ireland, having given the title to the earl of Ulster only the day before. Edward went to Bristol with Piers and Margaret to see them off to Ireland; they sailed on 28 June, three days late.
Even before Piers' departure, Edward was exerting himself to get the exile overturned. On 16 June, he granted the castle of Blanquefort in Gascony to the Pope's nephew and namesake Bertrand de Got, candidly explaining that he hoped the grant would encourage the Pope to look on Edward's affairs, i.e., Piers Gaveston, more favourably. It took a while, but a few months later, Pope Clement agreed to nullify the archbishop of Canterbury's threat to excommunicate Piers.
Edward spent the next few months schmoozing his earls and barons, granting them lands, favours, positions and money: "he bent one after another to his will, with gifts, promises and blandishments" (Vita). One by one, he brought then back to his side, to the disgust of the Vita: "See how often and abruptly great men change their sides…The love of magnates is as a game of dice." Labouring under the delusion that Edward and Piers would change their behaviour if Piers returned, the earl of Lincoln - formerly their most determined opponent - even persuaded some of the other earls to accept Piers' return.
Piers Gaveston came back to England on or about 27 June 1309, a year almost to the day since he'd left, having done a pretty good job as Lieutenant of Ireland. On 5 August 1309, at parliament in Stamford, the lands of his earldom were restored to him. Secure in Edward's favour and in the knowledge that the king had spent a year trying to bring him back, and therefore adored him as hopelessly as ever, Piers became ever more arrogant, and gave the earls insulting nicknames.
He and Edward then proceeded to demonstrate that neither of them had learned a damn thing from the experience, and that they did not have a molecule of political sense between them. Actually, that's not quite true. Edward's actions in 1308 and 1309 demonstrate clearly how astute, cunning and energetic he could be when he chose. But most of the time, he chose not to be. He couldn't be bothered unless his friends and therefore his personal feelings were involved, which must have been intensely frustrating to his contemporaries. If he had used his undoubted talents to, you know, actually govern his kingdom and to fight in Scotland, he could have been a great king.
As it was, events led inexorably to Piers' third and final exile, in November 1311, and ultimately, Edward's passion for and obsession with Piers led to his friend's destruction...